RUMEN DEVELOPMENT, INTESTINAL GROWTH AND HEPATIC METABOLISM IN THE PRE-AND POST-WEANING RUMINANT

Authors: Baldwin, Ransom - Randy; MCLEOD, K - UNIVERSITY OF KENTUCKY; KLOTZ, J - UNIVERSITY OF TENNESSEE; HEITMANN, R - UNIVERSITY OF TENNESSEE

Submitted to: Journal of Dairy Science
Publication Type: Review Article
Publication Acceptance Date: 10/26/2003
Publication Date: 5/10/2004
Citation: Baldwin, R.L., Mcleod, K.R., Klotz, J.L., Heitmann, R.N. 2004. Rumen development, intestinal growth and hepatic metabolism in the pre-and post-weaning ruminant. Journal of Dairy Science. 87:E. Suppl.:E55-E65.

Interpretive Summary: The role of intestinal development and the process of transitioning calves from their neonatal reliance on nutrients supplied by milk to nutrients supplied from grain are of substantial economic importance to the producer. Improvements to the calf nutritional regime can decrease mortality and disease susceptibility, increase post-weaning rate of gain, and ultimately, enhance the rate of herd genetic improvement (due to increased capacity for voluntary culling). Current feeding practices result in weaning from milk by 3 to 4 weeks of age by daily encouragement to eat grain diets. Although the mechanisms are not yet completely understood, development of a viable fermentation within the rumen is required to initiate the maturation of the rumen epithelia. The metabolic ramifications of this transition to calf growth rate are great, as tissues must convert from reliance on glucose supplied from milk to the metabolism of volatile fatty acids as primary energy substrates. This transition is the result of differential expression of numerous genes regulating both physical and metabolic characteristics of the tissue. While the most dramatic physical changes occurring during development are associated with the rumen epithelium, changes in intestinal mass and metabolism are also realized in response to dietary changes. Amino acid use by the intestinal tissues is high and may affect amino acid availability in support of growth. Moreover, because the metabolic and protein synthetic activities of the digestive tract are high, accounting for up to 30% of both whole animal energy use and whole animal protein synthesis, understanding their regulation is vital to the continued improvement in calf management. Specific nutrient-gene interactions have been identified across the digestive tract which serve to increase visceral organ mass and directly change nutrient metabolism by the epithelia. Similarly, humoral factors have been identified as having regulatory function over gastrointestinal tissue mass and metabolism. These and continuing efforts to better understand the factors affecting intestinal development will improve weaning strategies and foster better post weaning calf growth performance.

Technical Abstract: The role of intestinal development and the process of transitioning calves from their neonatal reliance on nutrients supplied by milk to nutrients supplied from grain are of substantial economic importance to the producer. Improvements to the calf nutritional regime can decrease mortality and disease susceptibility, increase post-weaning rate of gain, and ultimately, enhance the rate of herd genetic improvement (due to increased capacity for voluntary culling). Current feeding practices result in weaning from milk by 3 to 4 weeks of age by daily encouragement to eat grain diets. Although the mechanisms are not yet completely understood, development of a viable fermentation within the rumen is required to initiate the maturation of the rumen epithelia. The metabolic ramifications of this transition to calf growth rate are great, as tissues must convert from reliance on glucose supplied from milk to the metabolism of volatile fatty acids as primary energy substrates. This transition is the result of differential expression of numerous genes regulating both physical and metabolic characteristics of the tissue. While the most dramatic physical changes occurring during development are associated with the rumen epithelium, changes in intestinal mass and metabolism are also realized in response to dietary changes. Amino acid use by the intestinal tissues is high and may affect amino acid availability in support of growth. Moreover, because the metabolic and protein synthetic activities of the digestive tract are high, accounting for up to 30% of both whole animal energy use and whole animal protein synthesis, understanding their regulation is vital to the continued improvement in calf management. Specific nutrient-gene interactions have been identified across the digestive tract which serve to increase visceral organ mass and directly change nutrient metabolism by the epithelia. Similarly, humoral factors have been identified as having regulatory function over gastrointestinal tissue mass and metabolism. These and continuing efforts to better understand the factors affecting intestinal development will improve weaning strategies and foster better post weaning calf growth performance.